Inverting a signal cancels sound at all frequencies when paths are equal
Evidence
The idea seems to have originated with Goertz et al. (2001), who used an arrangement of subwoofers on the front wall, generating an approximation of a plane wave that propagates to the rear of the room where a similar arrangement of subwoofers, appropriately delayed and polarity inverted, cancels the wave when it arrives. Ideally this eliminates standing waves and everyone in the room should hear good bass. It requires a perfectly rectangular room and at least four subwoofers to work well. The scheme was called double bass array (DBA). — Toole, Floyd E, Sound reproduction- the acoustics and…, 1604 (
#exemplifies, via linked claim)
Categorization
- XREF: connects to: Superposed sounds cancel or amplify locally without changing each other; Inverted signals cancel at all frequencies while delayed signals cancel selectively by frequency; Subwoofer mode cancellation needs no equalization to fix boom (+3 more)
Broader Connections
- Delayed, inverted subwoofer arrays can cancel standing waves in rectangular rooms
#exemplifies(0.95) — Toole, Floyd E, Sound reproduction- the acoustics and…, 1604 - Active noise cancellation fails at high frequencies due to phase shift limits
#qualifies(0.85) - Active noise cancellation dominates below 1 kHz while passive isolation takes over above it
#qualifies(0.80)